Controversy exists as to the role of age of asthma onset in childhood asthma. Data collected on self-reported physician-diagnosed asthmatics ages 6-24 yrs (N=352), who participated in the second National Health and Nutritional Examination, 1976-1980, a national cross-sectional sample, were examined to see if age at onset had a prognostic role in the future course of the asthma. Late-onset asthma was defined as onset of symptoms at or after the third birthday. Late-onset asthmatics reported more allergic rhinitis OR=1.73 (95% CI 1.03, 2.83), and were more likely to have at least 1 positive prick-puncture allergen skin test OR=1.79 (95% CI 1.06, 3.03). Late-onset asthmatics tended to report more problems during the past 12 months with wheezing 1.44 (95% CI 0.9, 2.32) and sinusitis 1.59 (95% CI 0.8, 3.17). No difference was found in pulmonary function tests, reported chronic rhinitis, reporting asthma to be active, reported other allergies, problems within the last 12 months with cough attacks, or during the past 3 years a period of cough and phlegm lasting more than 3 weeks. The role allergy plays in the severity among late-onset asthmatics requires additional investigation.